1. Field of the Invention
The invention relates in general to apparatus for continuously coating an elongated metallic member, and more specifically to such apparatus which initially applies the coating to the conductor in dry powder form via electrostatic techniques.
2. Description of the Prior Art
Copper and aluminum wire have conventionally been coated in multiple-pass vertical coating towers using solvent base coating materials. The energy requirements in such a coating facility are quite high, and the solvent may present safety and pollution problems unless properly dealt with. The high energy costs and costly safety and anti-pollution apparatus for dealing with the solvent have made it economically attractive to consider alternate arrangements for applying an insulating coating on a continuously moving wire.
The electrostatic dry powder technique is particularly attractive, as solvents are not used, and a coating of the desired build or thickness may be applied to the wire in a single pass. The energy requirements are substantially lower, compared with using solvent base materials, only requiring that the wire be heated to the focusing and curing temperature of the particulated deposit on the wire.
If an existing solvent base coating facility is converted to an electrostatic wire coating facility, the wire is necessarily coated while moving vertically. The vertical orientation of the wire through a cloud of electrostatically charged particles promotes a uniform deposit on all sides of a rectangular wire, but it also presents certain problems. The line speed is limited by the cloud height, which has a certain practical limitation due to gravity. A horizontal facility does not have this limitation. A horizontal powder coating facility is felt to offer other advantages over a vertical facility, such as reduced scrap, easier operator control and maintenance, and better control of the coating build dimension. Also, a new horizontal powder coating facility may be installed for lower capital facility cost than a new vertical powder coating facility. The horizontal powder coating facility, however, presents certain problems in achieving build uniformity about the circumference of the wire, and the problem is compounded when the wire has a rectangular cross-sectional configuration.
U. S. Pat. No. 3,248,253 discloses a horizontal powder coating facility in which a grounded wire passes over a bed of electrostatically charged particles, which creates a cloud of particles above the bed due to the difference in the electrical potential between the charged particles and the grounded wire.
U. S. Pat. No. 3,396,699 discloses a horizontal powder coating facility which is directed to controlling the build dimension on the wire by adjustable barrier tubes which control the effective length of the cloud chamber, and a blower to dislodge non-electrostatically attracted particles from the wire.
U. S. Pat. No. 3,560,239 discloses a horizontal powder coating facility which includes applying and drying a primer coating to the wire prior to an electrostatically applied coating.
U. S. Pat. No. 3,566,833 discloses a horizontal powder coating facility which includes a spray gun in the coating chamber along with a fluidized bed of electrostatically charged particles.
U. S. Pat. No. 3,865,079 discloses a horizontal powder coating facility directed to an arrangement for electrostatically charging the powder.
U. S. Pat. No. 3,916,826 discloses a vertical powder coating facility directed to an arrangement for charging the powder.
Application Ser. Nos. 648,444 and 678,579, filed Jan. 12, 1976 and Apr. 20, 1976, respectively, which are assigned to the same assignee as the present application, disclose vertical powder coating facilities directed to arrangements for controlling the coating thickness, and for producing a more uniform coating on the wire, respectively.